This project approaches normal CNS myelin formation by studying hypomyelinating mutations in the mouse genes for myelin basic protein, MBP, and proteolipid protein, PLP, the target of human Pelizaeus- Merzbacher's disease. Unique colonies in which all the mutations are maintained on the same congenic hybrid stock provide genetic control for comparing mice bearing one mutation at a time with double mutant and mutant-transgene construct mice, using quantitative and developmental morphology, cell and tissue culture, protein immunochemistry, and now molecular biology. The MBP and PLP genes code, not only for major myelin proteins, but also for unknown developmental functions which may be carried out by alternately spliced isoforms of the proteins, and are reflected in the mutants by alterations of oligodendrocyte (OL) morphology, of OL viability, or animal lifespan. The construct mouse studies show these developmental functions are regulated independently from bulk structural protein synthesis. In the requested project period, studies will, focus on: 1. A new PLP mutation unique to this laboratory, jp(4J), with a single base change producing an alanine-serine change at position #38, remote from other murine PLP mutations. It produces the greatest hypo- myelination and earliest death of a single mutant mouse. 2. A new strain of the well-studied PLP mutation jp(msd), also unique, which produces longer-lived affected animals than the standard strain. 3. Collaborative immunochemical studies, with Dr. Charissa Dyer, of dissociated cultured oligodendrocytes (OLs). In wild-type OLs, Dyer has described complex patterns of localization and stimulus-specific relocalization of OL-specific constituents. OLs from MBP mutant and transgenic animals now show major abnormalities of both localization and relocalization. This is strong evidence that MBP functions as a link in an intracellular signalling system. Such studies will advance our understanding of the nature and mechanism of the independently regulated gene functions.